This invention relates to a hectographic printing process, and more particularly, to a process for preparing hectographic printing masters.
Hectographic printing is one of the conventional printing processes and is especially convenient when reproductions of more or less than one hundred sheets are required. In the hectographic process, a printing master is provided by depositing a sprit process ink on a suitable master substrate. More specifically, an original is delineated on ordinary paper (the master substrate) covered with a specific carbon tissue (coated with a sprit process ink) with a pencil, a typewriter and the like, thereby depositing the ink onto the rear surface of the master substrate. Alternatively, a thermal transferring process can be used for the above purpose. According to this method, heat radiation is applied to the carbon tissue superposed with such an original having thereon an original image colored in black, thus causing the ink to be deposited on the master substrate. Such hectographic printing master is then applied onto a paper for reproduction with the exertion of slight pressure. During such exertion, a dye included in the ink deposited on the master is dissolved into alcohol coated on the paper for reproduction. Thus, during each reproduction operation, a small amount of the ink from the master is deposited in an image configuration on the particular paper. Various kinds of sprit inks for such purpose have already been proposed. However, all of these inks have the disadvantage that the viscosity thereof is rather high. The typical ink comprises a vegetable wax, a dye such as a crystal violet and an oil, and such consequent ink ordinarily has a high viscosity such as some hundreds c.P. at 100.degree. C. Since the hectographic process indispensably includes a step of depositing the sprit process ink on the rear surface of the master substrate as stated above, a troublesome manual step must be involved. Thus, the handling of the carbon tissue makes the operator's hands dirty. Further, since the sprit carbon tissue can not be reused, the hectograph inherently involves the disadvantage that it can not be accomplished at low cost. Also, in the case where the original is prepared by handwriting or by typographical writing, even consequent reproduction brought about by a thermal transferring process results a poor resolving power, in which the visual line density on the reproduction is at most two to three lines per millimeter.
To cope with these disadvantages, there may be considered the use of an ink jet generating unit. However, it has not been possible to find a hectographic ink suitable for such unit. Furthermore, when one of the conventional apparatuses for preparing printing masters is employed, the following requirement specific to hectographic printing masters must be taken into consideration.
That is, a conventional ink jet generating apparatus comprises a first drum on the circumference of which is wound the original, and a second drum on the circumference of which is wound recording paper. In accordance with the rotation of the first drum, a detecting means including, for example, a photoelectric element is adapted to correspondingly shift along the rotating axis of the first drum, thereby to scan the whole surface of the original. The second drum is also adapted to rotate in association with the rotation of the first drum, while a recording member with a needle electrode is also adapted to be shifted along the rotating axis of the second drum in a manner such that the image of the original is synchronously formed as a similarly oriented image on the recording paper. In adapting such apparatus to hectographic printing, the consequent recording paper bearing the image thereon would be used for the printing master. However, according to the hectographic printing process, a mirror image is required for the image on the recording paper, since the image carrying surface of the recording paper would be directly applied onto the paper for reproduction, with the ink forming the image configuration being deposited onto the paper for reproduction. Thus, when a hectographic printing master is prepared with such conventional apparatus, there must be further provided a specific signal storing circuit. Namely, such signal storing circuit must store signals of the image concentration of the original, and upon preparing the master the signals thus stored are adapted to be output in an opposite manner relative to the inputting succession thereof. Such being the case, in addition to the signal storing circuit, signal control circuit means is indispensable to control such input and output signals. Thus, the consequent apparatus including these appliances becomes quite expensive, with the construction thereof being quite complex.